High frequency energy interchange device



Nov. 6, 1962 G. c. VAN HOVEN HIGH FREQUENCY ENERGY INTERCHANGE DEVICE Filed April 28, 1959 INVENTOR. BY M United States Patent @fitice 3,052,983 Patented Nov. 6, 1 962 3,062,983 HIGH FREQUENCY ENERGY INTERCHANGE DEVICE Gerard C. Van Hoven, Palo Alto, Calif., assignor to General Electric Company, a corporation of New York Filed Apr. 28, 1959, Ser. No. 809,444 3 Claims. (Cl. 3l5--3.6)

This invention relates to high frequency energy inter change devices of the type which rely upon an interchange of energy between a stream of electrons and electromagnetic waves produced by radio frequency fields in the region of the electron stream. More particularly, the invention relates to such a device wherein the electromagnetic waves are propagated along a slow-wave transmission line of the helix or helix-derived type and has as an important feature the provision of an improved arrangement for coupling the circuit helix or helices of the device to input and output transmission lines of the standard rectangular waveguide type.

In a conventional traveling-wave amplifier tube of the helix type, an electron stream is projected along an elongated helix at a velocity approximately equal to the axial phase velocity of electromagnetic waves traveling along the hel x. By successive processes of electron velocity modulation and inductive output (magnetic induction), the stream is modulated by the electric field set up along the helix by the electromagnetic wave, and the modulated stream gives up energy to the wave to increase its amplitude.

One of the important problems in the design of traveling-wave amplifiers is the problem of introducing electromagnetic waves onto the slow-wave transmission line from an input line such as a common waveguide of rectangular cross section and extracting the amplified electromagnetic waves from the transmission line. It is characteristic of traveling-wave amplifiers that interaction between the electron stream and the circuit takes place over an extremely wide band of frequencies and it is frequently found that the useful range of frequencies of the amplifier is limited by the transducers or coupling between a waveguide and the slow-wave circuit. As a consequence, it is extremely desirable to have a coupling means or transducer which is at least as broad band as the traveling-wave amplifier itself. Another desirable characteristic of the transducer is that it have high power handling capabilities, particularly since the output transducer is the only place Where the full radio frequency power developed by the amplifier actually occurs. Accordingly, it is an object of the present invention to provide a high frequency energy interchange device of the traveling-wave type with a transducer to provide coupling between one or more helical transmission lines and a rectangular waveguide which transducer will couple a wide band of frequencies and be capable of handling high powers.

Another difficult problem encountered in constructing such devices is that of making the structure suificiently rugged to withstand the rigors of assembly and the shocks and vibrations which the tube may be subject to in use. Since the slow-Wave transmission lines in such devices and the transitions between the slow-wave transmission line and input and output waveguides are generally at least as delicate as any other part of the structure, they are most in need of ruggedization. Moreover, the coupling efliciency is often critically dependent upon the exact transducer configuration so that rigidity of dimension is quite important.

Accordingly, it is another object of the present invention to provide, in a high frequency energy interchange device of the travelingwave type, a transition between conventional Waveguide and a slow-wave transmission line which is extremely rugged and acts as a support for the transmission line.

In carrying out the present invention, a high frequency energy interchange device of the traveling-wave type is provided and support for the slow-wave transmission line as well as coupling of electromagnetic waves between the helical slow-wave transmission line and input and output waveguides is provided by extending a conductive transducer element (antenna) across the waveguide in question and securing it to more than one of the end turns of the slow-Wave transmission line.

The novel features which are believed to be characteristic of the invention are specifically set forth in the appended claims. The invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which:

FIGURE 1 is a partially broken away side elevation of a traveling-wave amplifier which incorporates the present invention;

FIGURE 2 is a transverse section through the input waveguide taken on line 22 of FIGURE 1 and looking into the end of the slow-wave circuit;

FIGURE 3 is an enlarged and partial, central, vertical, longitudinal section through the input end of the traveling-Wave tube of FIGURE 1 as projected from line 33 of the transverse section of FIGURE 2 and omitting part of the slow-wave transmission line to illustrate in detail the input coupling of the present invention;

FIGURE 4 is a perspective view of the coupling pin utilized at the input and output of the traveling-wave amplifier; and

FIGURE 5 is an enlarged and detailed view showing an end view of the helical slow-wave transmission line with a coupling pin in place to illustrate the coupling configuration.

In FIGURE 1 of the drawing, a traveling-wave tube is illustrated. The traveling-wave tube includes an envelope 10 which serves as a vacuum enclosure. As illustrated, the envelope 10 has an enlarged cylindrical ceramic gun enclosing portion 11 at one end, a long metallic cylindrical portion 12 forming the central part, and enlarged cylindrical metal and ceramic collector portion 13 forming the opposite end. The central elongated cylindrical metallic portion is connected to the enlarged ceramic portions 11 and 13 at its opposite ends by input and out- .put metallic waveguides 14 and 15, respectively. The input and output waveguides 14 and 15 are of rectangular cross section and extend across the cylindrical structure with their longitudinal axes perpendicular to the longitudinal axis of the cylindrical envelope 10.

The small cylindrical central portion of the envelope it; houses the interaction transmission line 16, the enlarged cylindrical ceramicportion 11 at the input end of the device, i.e., adjacent the input waveguide 14, houses an electron gun (not shown) which is designed to produce the desired electron streams, and the enlarged metal ceramic portion 13 at the output end of the device serves to collect electrons from the electron streams projected down the length of the device, thereby to dissipate residual energy in the streams. Thus, the electron gun projects electron streams down the length of the slow-wave trans, mission line 16 in such a manner that they interact with the electromagnetic waves propagated down the slow-wave transmission line 16 to produce amplification. Electrons from the stream which pass through the helical transmission line 1d are collected inside the enlarged metalceramic collector portion 13.

The electron gun structure enclosed by the enlarged ceramic portion 11 is not illustrated and described in detail since the specific structure doesnot constitute a:

d, part of the present invention. One particular structure for producing four parallel electron streams may be comprised of four side-by-side and independent electron guns of conventional design and the streams from these guns may be focused over their entire length by producing a magnetic field axially along the structure. That is, the space charge of the electrons in the streams may be prevented from spreading the electrons to such an extent that they pass out of the interaction region and intercept the slow-wave transmission line by producing such a magnetic field axially along the structure. This is typically done by providing a long annular solenoid (also not shown) which surrounds the transmission line enclosing portion 12 of the tube and is concentric therewith. To simplify the present drawing and description, a magnetic field producing solenoid is not illustrated.

For an understanding of the exact configuration of the slow-wave transmission line 16 illustrated, reference may be had to FIGURES 2 and 5. From these figures, it is seen that the slow-wave transmission line 16 is a composite slow-wave structure consisting of four helical conductors 17, 18, 2G and 21, each having the same diameter, pitch and axial length. The helical conductors 17, 18, Ztl and 21 are arranged so that their axes form the long parallel sides of an elongated rectangular parallelepiped, the other sides of which are equal to the diameter of the individual helices. Each of the helical conductors is illustrated as being wound in the opposite sense to the immediately adjacent conductors. That is, the diametrically opposed helical conductors (2t) and 17) in the parallelepiped on the upper and lower corners thereof are wound right-handed as indicated by arrows adjacent each of the conductors and the two conductors 18 and 21 on the remaining two corners are wound left-handed, also as indicated by the arrows adjacent the conductors. But of course, they all may be wound in the same sense if desired. With the arrangement illustrated, each helical conductor contacts two adjacent helical conductors at points (on turns) along their length that are spaced a turn apart and are preferably brazed together at each point of contact. The reason for utilizing such parallel helical conductors is set forth in detail in the John L. Putz application, Serial Number 657,367, filed May 6, 1957, entitled Electron Discharge Devices, and assigned to the assignee of the present invention. Consequently, the characteristics of the circuit 16 are not discussed in detail. However, it is well to note that the invention is not limited to the specific circuit 16 illustrated but is shown in connection with this circuit since it is utilized to such advantage with this particular arrangement.

Since the four helical conductors 17, 18, 20 and 21 are brazed together turn to turn down their length, it is convenient to support them in the cylindrical barrel or transmission line enclosing portion 12 of the envelope by four rods 22 of dielectric .material, such as sapphire or quartz, which are of substantially circular cross section. Each of the rods 22 extends down the length of the slowwave transmission line 16 in contact with two adjacent helical conductors so that the center lines of the rods 22 form the parallel sides of an elongated rectangular parallelepiped which sides are displaced 45 degrees with respect to the elongated sides of the parallelepiped defined by the longitudinal axes of the conductors 17, 18, and 21.

It is noted that the opposite ends of the slow-wave transmission line 16 and the supporting dielectric rods 22 extend into the input and output waveguides 14 and 15. In the wall of the input and output waveguides 14 and 15, directly opposite the ends of the transmission line 16, input and output transmission line supporting and beam passing cylindrical conductive plugs 23 are provided. Since both of these plugs 23 are identical and serve the same general purpose, only the plug 23 at the input end of the envelope It and its associated structure are illustrated in detail (see FIGURES l and 3).

In order to provide a path for each of the electron streams to pass down the full length of the envelope 10, the supporting plugs 23 are provided with four beam passing apertures 24 spaced equidistant around the center of the cylindrical plug 23. The plug 23 at the input end of the envelope 10 is positioned in a cylindrical aperture 25 provided in the wall of the input waveguide 14 which is opposite the metallic central portion 12 of the envelope with its four beam passing apertures in register with the electron streams from the four electron guns and the central axes of the four helical conductors 17, 18, 20 and 21 of the slow-wave transmission line 16. The support plug 23 is fixed in position in the input waveguide 14 by brazing.

The support plug 23 at the output or collector end of the envelope 10 is fixed in position in the same manner with its beam passing apertures 24 also in register with the axes of the helical conductors 17, 18, 20 and 21. Thus, electron streams may be directed down the length of each of the helical conductors 17, 18, 20 and 21 of the transmission line 16 and out through the output supporting plug 23 into the collector section 13.

In addition to the four electron stream apertures in the input and output plugs 23, there is provided a centrally located aperture 26 which is provided for the purpose of receiving and holding a wave coupling and transmission line supporting pin 27. The specific configuration of the coupling pin 27 is not too critical. However, as may best be seen in FIGURE 4, the pin 27 has one cylindrical end 28, an intermediate shoulder 30, which is slightly larger than the cylindrical portion 28 of the pin, and a substantially square end 31. As illustrated, the substantially square end 31 is formed by chamfering four flat sides on cylindrical stock of the same diameter as the opposite end portion 28. The round end 28 of the pin 27 is positioned within the centrally located aperture 26 in the beam passing and transmission line supporting plug 23 and extends across the input or output waveguide. The four sided end 31 of the pin 27 projects in between the individual helices of the main transmission line 16 so that the intermediate shoulder 30 abuts the end turns of the helices. At least the first two turns of each of the helices 17, 18, 20 and 21, that is, the two end turns of the helices at both of their opposite ends are brazed to the pin 27 which projects between the turns. In this manner, electromagnetic energy introduced into the input waveguide 14 is impinged upon the coupling pin 27 at the input end of the device which is brazed to the first two turns of each of the individual helices and coupled or transferred onto the slow-wave transmission line 16. The wave 18 propagated from the gun end of the tube toward the output or collector end and interaction takes place between the wave and the electron streams in the conventional manner. The amplified radio frequency energy impinges on the coupling pin 27 at the output end of the envelope 10 and is thereby coupled to the output waveguide 15.

The coupling thus provided has proved to be capable of a fifty percent band width with excellent mechanical and thermal qualities. This particular coupling arrangement effectively lengthens the helical transmission line 16 as far as its heat conduction properties are concerned and increases its mass in the region of the transition. Further, the arrangement greatly increases the rigidity of the configuration in the regions in which its shape is most important.

The cylindrical gun enclosing ceramic portion 11 is provided at its outer end with a metallic flange 32 brazed thereto and a disc-shaped metallic end cap 33 heliarced to the flange 32 to provide a vacuum tight seal for the outer end of the ceramic gun enclosing portion. At its opposite end, the gun enclosing ceramic portion 11 is provided with a cup-shaped flange 34 which extends outwardly from the outer periphery of the cylindrical ceramic and back towards the outer end of the ceramic cylinder 11. This cup-shaped flange 34 is concentric with the ceramic cylinder. 11.-and-is provided for purposes of alignment. A matching cup-shaped metallic flange 35 is brazed to the outer end or outer wall of the input waveguide 14 in such a manner that it is concentric with the aperture 25 therethrough provided for the transmission line supporting and beam passing end plug 23. Thus, the cup-shaped flange 34 around the outer periphery of the ceramic gun enclosing portion 11 may be fitted snugly within the cup-shaped flange 35 on the input waveguide and heliarced thereto in a man her to form. a vacuum tight seal.

The central cylindrical transmission line enclosing portion 12 of the envelope It) is sealed at its opposite ends in a vacuum tight manner to both the input and output waveguides. The opposite wall of the output waveguide 15 is, as previously described, provided with an aperture 25 of the proper size to receive a transmission line supporting and beam passing plug 23. A concentric metal cup-shaped flange 36 is provided around this aperture 25 for the purpose of receiving and aligning the collector section 13 of the envelope on the outer Wall of the output waveguide 15.

The collector section 13 of the traveling-wave tube is not illustrated in great detail since its specific configuration does not constitute a part of the present invention. However, as illustrated in FIGURE 1, the collector includes a hollow cylindrical conductor member 37 which is provided for the purpose of collecting the electrons from the electron streams. The collector member 37 is provided with a cup-shaped flange portion 38 whfch extends outwardly from one end of the main body portion forward toward the tube envelope 10. A hollow tubular ceramic member 40 is brazed inside the flange 36 on the outer Wall of output waveguide at one end and inside the cup-shaped flange 38 on the collector member 37 to provide a vacuum tight seal and also to insulate the collector 37 from the conductive output waveguide 15.

The enclosure is made vacuum tight by providing vacuum tight ceramic windows (not shown) at the outer ends of the input and output waveguides 14 and 15.

Thus, in accordance with the principles of the invention, a traveling-wave tube is provided with an extremely broad band coupling between the transmission line and input and output waveguides which coupling has the advantages of being extremely rugged, rigidly supporting the ends of the tube transmission line and providing excellent heat dissipating properties.

While a particular embodiment of the invention has been described and illustrated, it will, of course, be understood that the invention is not limited thereto, since many modifications, both in the circuit arrangement and in the instrumentalities employed, may be made. It is contemplated that the appended claims will cover any such modifications as fall within the true spirit and scope of the invention.

What I claim is new and desire to secure by Letters Patent of the United States is:

l. A transducer for coupling electromagnetic waves between a rectangular waveguide having two broad walls and two narrow walls and a slow-wave transmission line which includes four helical conductors arranged side by side with parallel longitudinal axes and turns along the length of each helical conductor connected to corresponding turns on the two adjacent helical conductors to form an array defining a space therebetween, the rectangular waveguide being provided with an aperture through at least one broad wall, said slow wave transmission line being positioned with its longitudinal axis perpendicular to the plane of the said one broad wall of said rectangular waveguide and one end protruding through the aperture therein, said transducer including a coupling pin positioned with its longitudinal axis parallel to the longitudinal axis of said slow wave transmission line and one end in the space provided therebetween and electricallyand mechanically connected to at'least two end turns on each of said transmission lines and extending across the waveguide with its opposite end fixed to the opposite broad wall of said waveguide. g

2. In combination in a high frequency energy interchange device of the traveling-wave type, an elongated evacuated envelope containing an elongated slow-wave transmission line, said slow-wave transmission line including four helical conductors arranged side by side with parallel longitudinal axes and turns along the length of each helical conductor connected to corresponding turns on the two adjacent helical conductors to form an array with a space therebetween; electron gun means close to one end of said transmission line for projecting a stream of electrons down the axis of each helical conductor for interaction with electromagnetic waves propagated therealong; a collector at the opposite end of said transmission line for collection of electrons; individual input and output waveguides of rectangular cross section extending transverse to said traveling-wave tube between said transmission line and said gun and said transmission line and said collector, respectively, for

the purpose of introducing and extracting electromagnetic waves, said input and output waveguides being provided with an aperture through the broad walls in alignment with said transmission line and electron gun means, said transmission line positioned with its longitudinal axis perpendicular to the plane of the broad walls of each of said input and output waveguides with one end protruding through the aperture in the adjacent broad wall; input and output coupling means positioned at opposite ends of said slow-wave transmission line, each coupling means including a coupling pin positioned with its longitudinal axis parallel to the longitudinal axis of said slow-wave transmission line and one end in the space provided therebetween and electrically and mechanically connected to at two end turns on at least one of said helical conductors and extending across the adjacent rectangular waveguide with its opposite end fixed to the opposite broad wall of the respective waveguide.

3. A high frequency energy interchange device of the traveling-Wave type including in combination an elongated evacuated envelope containing an elongated slowwave transmission line, said slow-wave transmission line including four helical conductors arranged side by side with parallel longitudinal axes and turns along the length of each helical conductor connected to corresponding turns on the two adjacent helical conductors to form a cluster with a space therebetween; electron gun means close to one end of said transmission line for projecting a stream of electrons down the longitudinal axis of each helical conductor for interaction with electromagnetic waves thereon; a collector at the opposite end of said transmission line for collection of electrons; input and output waveguides of rectangular cross section extending transverse to said traveling-wave tube between said transmission line and said gun and said transmission line and said collector, respectively, for the purpose of introducing and extracting electromagnetic waves, said input and output waveguides being provided with an aperture throughbroad walls in alignment with said transmission line and electron gun means; individual coupling and supporting plugs having a centrally located aperture and four electron stream passing apertures spaced equidistant therearound, said individual plugs positioned in the apertures provided in the broad wall of said input and output waveguides which are adjacent said electron gun means and said collector, respectively, with each of said stream passing apertures disposed to pass an electron stream, said transmission line positioned with opposite ends protruding through an aperture in the adjacent broad wall of said input and output waveguides with individual helical conductors coaxially disposed relative 7 to said stream passing apertures in said plugs; input and output coupling means positioned at opposite ends of said slow-wave transmission line, each including a coupling pin positioned with one end in the space provided between helical conductors and electrically and mechan- 5 ically connected to at least two end turns in each of said conductors and extending across the adjacent input and output waveguides, respectively, with its opposite end positioned in the centrally located aperture of its respective coupling plug. m

References Cited in the file of this patent UNITED STATES PATENTS Pierce July 1,

Bohlke Sept. 16,

Jonker Apr. 16,

Robertson et a1. Jan. 28,

Rogers June 9,

FOREIGN PATENTS France Feb. 9,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,062,983 November 6, 1962 Gerard C. Van Hoven It is hereby certified that err ent requiring correction and that th corrected below.

or appears in the above numbered pate said Letters Patent should read as Column 6, line 37, after "at" first occurrence, insert least Signed and sealed this 9th day of April 1963.,

(SEAL) Attest:

ESTON G. JOHNSON Attesting Officer DAVID L. LADD Commissioner of Patents 

